Anne-Isabelle ETIENVRE Top quark physics Anne-Isabelle ETIENVRE

Outline Introduction Top quark discovery: a long search! Top-antitop production at hadron colliders Single top production Sensitivity to physics beyond Standard Model 16/09/08 A.-I.Etienvre-FAPPS 2008

Introduction (1/2) Identity card (a peculiar quark): SU(2)L partner of the bottom Q = 2/3, T3=1/2 Heaviest quark (gold atom!): 40 * m(bottom quark), Mtop = 172.5 ± 1.2 GeV/c2 (Tevatron) Produced predominantly (in hadron-hadron collisions) by strong interaction Width Gtop = 1-2 GeV/c2 (increases with top mass) Corresponding lifetime short = 0.5 x 10-24 s Top decays before hadronisation keeping its properties 16/09/08 A.-I.Etienvre-FAPPS 2008

Introduction (2/2) Identity card: For each measurement, we will see: Yukawa coupling ytop = 1 (mtop = yt v2) Decays almost exclusively through t Wb: In the Standard Model, 99.9% i.e. CKM matrix |Vtb|1 For each measurement, we will see: Why it is interesting to be performed Where do we stand What we should learn with LHC 16/09/08 A.-I.Etienvre-FAPPS 2008

Motivations for top quark physics studies Top quark exists and will be produced abundantly In Standard Model (SM): top- and W-mass constrain Higgs mass through radiative corrections Scrutinize SM by precise determination of the top quark mass Beyond SM: new physics? Many heavy particles decay in tt Handle on new physics by detailed properties of top Experiment: top quark useful to calibrate the detector Commissioning (jet energy scale, b-tagging,..) Beyond top quark: Top quarks will be a major source of background for many searchs (Higgs, SUSY, exotics,…) 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark discovery (1975  1995) 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark discovery 1974 : 2 quarks and leptons families A third family 1974 : 2 quarks and leptons families 1975: t discovery (SLAC) a third family is needed! 1977 : b quark discovery (Y resonance ) μ+μ- spectrum b quark should have an electroweak partner : the top quark 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark discovery Direct searches: Search for a toponium (bounded state t t) around 27 GeV/c2 top mass expected around 15 GeV/c2 (mass s/c/b : 0.5/1.5/4.5 -> mtop~15 GeV/c2) Search at the e+e- colliders: DESY-PETRA (1980) :  s = 12 -36 GeV  mtop > 30 GeV/c2 LEP 1 (1989), study of Z t t , with  s = 91 GeV  mtop > 45.8 GeV/c2 Search at the p p̅ colliders: UA1 and UA2 (1981 -> 1990) ,  s = 640 GeV  mtop > 69 GeV/c2 « discovery » by UA1 in 1984 (mtop= 40 GeV/c2) : 9 signal evts / 0.2 background evts (background was underestimated) Tevatron (1990  1992),  s = 1.8 TeV  mtop > 91 GeV/c2 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark discovery Discovery : Tevatron (1995) Indirect searches: mtop = 176 ± 8 (stat.) ± 10 (syst.) GeV/c2 (CDF) mtop = 199 ± 19(stat.) ± 22 (syst.) GeV/c2 (D0) Indirect searches: Precise electroweak measurements correlated to the radiative corrections: Dr = K mtop2 , Drrésiduel= f(ln(mH2)) 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark discovery Top mass evolution Tevatron discovery Current measurement 16/09/08 A.-I.Etienvre-FAPPS 2008

Colliders Tevatron (p p̅ ),  s = 1.96 TeV LHC (pp): s = 14 TeV Luminosity: 2.7 fb-1 summer 2008 20 pb-1 december 2008 ( s = 10 TeV) 7-8 fb-1 2009 1 fb-1 2009 ( s = 14 TeV) expected! Tevatron (p p̅ ),  s = 1.96 TeV LHC (pp): s = 14 TeV 16/09/08 A.-I.Etienvre-FAPPS 2008

Colliders Cross section comparison Tevatron/LHC Process Tevatron (pb) LHC (pb) tt̅ 6.8 833 bb̅ 2.8 104 2.2 107 W+2jets 1.3 103 18 103 WW 12.0 117 WZ 3.68 23 16/09/08 A.-I.Etienvre-FAPPS 2008

Colliders Comparison Tevatron/LHC ( s = 10 TeV) Luminosity Number of inclusive tt Number of W (lv)+jets (background) Start-up LHC ( s = 10 TeV) 20 pb-1 ≈ 16 000 ≈ 2.4 105 Low-luminosity LHC (2009) 1 fb-1 ≈ 800 000 ≈ 120 105 Tevatron (summer 2009) 5.1 fb-1 ≈ 35 000 ≈ 2.0 106 16/09/08 A.-I.Etienvre-FAPPS 2008

Total collected before start LHC Top pair production Opposite @ Tevatron Production (strong interaction): Cross section LHC NLO(tt) = 834 ± 100 pb Tevatron: 7 pb Comparison to other production processes @ LHC: ~90% gg ~10% qq process (pb) Total collected before start LHC bb 5108 109 Zee 1.5103 107 Wℓ (ℓ=e,μ) 3104 tt 830 104 H(130 GeV/c2) 1 ? LHC is (also) a top factory! 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark decay Standard Model: Branching ratio / main backgrounds Br(tWb)  100% Studies % products of W decay Branching ratio / main backgrounds In tt events: Background: QCD (bb̅) Large combinatorial background Clean but low BR Many unknowns Bkgd:Z+jets, W+ jets, Z+jets, WW+jets, QCD (bb̅) Golden channel: Good B.R. Clean sample (background = W+jets, Z+jets, diboson, QCD) 16/09/08 A.-I.Etienvre-FAPPS 2008

Systematic errors in top quark studies Jet energy scale (light jets / b-jets) LHC aim : jet energy knowledge better than 1 % light jet energy scale contribution: can be strongly reduced using an in-situ calibration based on the W mass constraint (see later on) B jet energy scale: Dominant jet energy scale Tevatron : estimated from Monte Carlo (global rescaling factor) LHC : could be estimated from data 16/09/08 A.-I.Etienvre-FAPPS 2008

Systematic errors in top quark studies Initial and final state radiations (ISR, FSR) ISR Enhancement of the combinatorial background Bias on the top quark mass (over-estimation of the jet energies in the final state) FSR : Bias on the top quark mass (under-estimation of the jet energies in the final state) Estimated on Monte Carlo at the Tevatron Could be estimated on data at LHC b-quark fragmentation error estimated changing the Peterson parameter (-0.006 ) within its theoretical uncertainty (0.0025) combinatorial background error estimated varying the background shape and size in the fitting procedure 16/09/08 A.-I.Etienvre-FAPPS 2008

Top-antitop production Mass measurement top-antitop cross section measurement 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark mass measurement Why do we need a precise measurement of mtop? The uncertainties on mtop, and mW are the dominating ones in the electroweak fit Precise measurement of mtop, mW  one can get information on the missing parameter mHiggs one can test the validity of the Standard Model Dr = K mtop2 , Drrésiduel= f(ln(mH2)) 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark mass measurement Present measurement (Tevatron, July 2008): Mtop= 172.4 ± 0.7 (stat.) ± 1.0 (syst.) Most accurate measurement in the l+jets channel 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark mass measurement Electroweak fit: The blue band plot Incidence of precision: On Da: On mtop: mtop (2007) = 170.9 ± 1.8 GeV (2007) On mW: if with the same central values , 33 24 76 + - = H m 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark mass measurement Electroweak fit: direct mtop and mw indirect mtop and mw 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark mass measurement Leptonic side Hadronic side At LHC : Lepton+jets channel Event selection: Direct hadronic top reconstruction: Pairing of the 2 light jets < hadronic W Association hadronic W  b-jet Typical selection efficiency: ~5-10%: Isolated lepton PT>20 GeV ETmiss>20 GeV ≥ 2 light jets and 2 b-jets with pT>40 GeV S/B: 10-4  30 for a generated top mass = 175 GeV/c2 : M(top) = 175.0 ± 0.3 GeV/c2 s(top) = 11.8 ± 0.3 GeV/c2 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark mass measurement Lepton + jets channel (cont.) Systematic uncertainties: Jet energy scale (JES): light jet energy scale constrained by an in-situ rescaling based on the W mass b jet energy scale: dominant source of uncertainty Statistical uncertainty will be quickly negligible; Error on the top mass = 1 to 3.5 GeV for a JES = 1 to 5 % 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark mass measurement In-situ light jet energy scale (LHC) Light jet energy scale using W constraint: Template histograms of the invariant mass mjj have been generated, from W  qq PYTHIA for several values of the energy scale a c2 (template – data) minimum a All jets are calibrated with a a can be evaluated % energy, and h Ratio E(light jet) / E(b jets) estimated on Monte Carlo 1% on JES is achievable with 1 fb-1 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark mass measurement Alternative measurements: Di-leptons 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark mass measurement Top quark mass measurement expected for 10 fb-1 l +jets di-lepton All-jets ATLAS (stat.) 0.05 0.04 0.18 (syst.) 1 1.7 3 CMS 0.3 0.5 0.2 1.3 1.1 4.2  Huge effort to be performed for JES in order to reach < 1 GeV 16/09/08 A.-I.Etienvre-FAPPS 2008

Cross section measurement Motivations for a precise measurement of s(tt): Sensitivity to new physics: Search for resonances Beyond Standard Model top decay Not seen up to now (Tevatron) Indirect top mass measurement First step = reconstruction of the tt final state (in common with top mass) 16/09/08 A.-I.Etienvre-FAPPS 2008

Cross section measurement Cross section estimation: Counting method: 16/09/08 A.-I.Etienvre-FAPPS 2008

Cross section measurement Present tt cross section measurement (Tevatron): Stat. syst. Lumi Stat. syst. Lumi. 16/09/08 A.-I.Etienvre-FAPPS 2008

Cross section measurement Studies at LHC Early measurement (100 pb-1) Counting method Di-lepton channel:(in % of the cross-section): Systematic uncertainties dominated by JES, ISR and FSR, luminosity L+jets channel (in % of the cross-section): Systematic uncertainties dominated by JES and ISR/FSR, luminosity ATLAS ATLAS 16/09/08 A.-I.Etienvre-FAPPS 2008

Top mass from tt cross section Assuming that tt production is governed by Standard Model, mtop can be extracted from s(tt) If Ds/s(theo.)  5%, and Ds/s(exp.)  5 %, Dmtop  2.6 GeV Not so far from direct measurements at the beginning of LHC 16/09/08 A.-I.Etienvre-FAPPS 2008

Single top production 16/09/08 A.-I.Etienvre-FAPPS 2008

Single top production Electroweak production of the top quark: 3 channels s channel: Cross section Tevatron = 0.88 ± 0.14 pb Cross section LHC : 10 ± 0.8 pb t channel : Cross section Tevatron = 1.98 ± 0.30 pb Cross section LHC: 245 ± 30 pb Wt channel : Cross sectionTevatron = 0.21 ± 0.03 pb Not reachable @ Tevatron Cross section LHC : 60 ± 15 pb 16/09/08 A.-I.Etienvre-FAPPS 2008

Single top production Interest of the measurement: Cross section proportional to |Vtb|2 : single top is a way to measure |Vtb| Irreducible background for many processes (Higgs, SUSY) Sensitivity to new physics Each of the processes have different systematic errors for Vtb and are sensitive to different new physics 16/09/08 A.-I.Etienvre-FAPPS 2008

Single top production Tevatron study: Challenge Low Cross sections Large background (W+ 2 jets) S and t channels can be observed, Wt not reachable Evidence for single top process at Tevatron in 2006 for the first time (both s and t channels) July 2008 results D0 will update its results with more statistic 16/09/08 A.-I.Etienvre-FAPPS 2008

Single top production At LHC: With 1 fb-1, an accurate measurement is foreseen in t and Wt channels; s channel could be seen with 10 fb-1, but difficult (background) The Wt channel should be observed for the first time A limit on |Vtb| will be extracted from this measurement Process s/s (1 fb-1) Systematic t channel 23 % Luminosity, b-tagging, JES, ISR/FSR Wt 20.5% s 52% Background, luminosity, b-tagging, JES, ISR/FSR 16/09/08 A.-I.Etienvre-FAPPS 2008

Physics beyond Standard Model In top – antitop production In single top production No evidence seen at Tevatron At LHC? 16/09/08 A.-I.Etienvre-FAPPS 2008

Physics beyond Standard Model In top pair production Search for heavy resonance in M(tt) Non Standard Model distribution of M(tt) would be a signal of heavy particle X  tt Interference from non SM process Would also appear as a deviation in ds(tt)/dm(tt) Example: Z’ search Z’ is an hypothetical massive boson (spin 1) predicted by several extensions of SM 16/09/08 A.-I.Etienvre-FAPPS 2008

Physics beyond Standard Model In top pair production Z’ search LHC: For mZ’ = 700 GeV/c2, Can be discovered if s > 11 pb for an inclusive decay -- >tt Likelihood analysis: No excess M(Z’) > 760 GeV @ 95% C.L. 16/09/08 A.-I.Etienvre-FAPPS 2008

Physics beyond Standard Model Sensitivity to charged Higgs: Context: In Minimal extension of Standard Model (MSSM): 2 Higgs doublet  5 Higgs boson (h,H,A,H+,H-) Charged Higgs could modify top decay (BR(t Wb)≠ 1) Can be searched in single top or in tt production 16/09/08 A.-I.Etienvre-FAPPS 2008

Physics beyond Standard Model Sensitivity to charged Higgs Example in tt production: mH+ < mtop 16/09/08 A.-I.Etienvre-FAPPS 2008

Physics beyond Standard Model Sensitivity to charged Higgs search in single top production: for H+ mass > mtop Leads to same final state as s-channel 16/09/08 A.-I.Etienvre-FAPPS 2008

Physics beyond Standard Model In single top production: Modification of the coupling (Flavour Changing Neutral Current : « FCNC »): tcZ, tcg, tcg,… Strongly suppressed in SM (BR  10-13 – 10-11) Less suppressed in MSSM (10-6 – 10-4) 16/09/08 A.-I.Etienvre-FAPPS 2008

Physics beyond Standard Model In single top production FCNC @Tevatron BR(tqg) < 0.03 @ 95% C.L. BR(tqZ) < 0.04 @ 95% C.L. BR(tqg) < 0.01 @ 95% C.L. FCNC @ LHC (1 fb-1) B.R. t->Zq 16/09/08 A.-I.Etienvre-FAPPS 2008

Top quark electric charge Never measured: should be 2/3, but -4/3 exist in non SM Tevatron (l+jets channel): measurement via b-jet charge measurement LHC : measurement should be achieved with 1 fb-1 jet e,m b-jet n B-jet MET Qt= - 4/3 e excluded @ 94% C.L. 16/09/08 A.-I.Etienvre-FAPPS 2008

W polarisation Goal: tt decay (l+jets) used for W polarisation study SM: 2 states of helicity: F- = 0.297, F0 = 0.703 (LO) 2 discriminant distributions: pT(lepton) angle(lepton, W) t b W Left-handed W (lW=-1 ) Longitudinal W (lW=0 ) Right-handed W (lW=+1 ) 16/09/08 A.-I.Etienvre-FAPPS 2008

W polarisation Results LHC: D0: CDF:  no evidence for physics beyond SM LHC: Polarisation measurement @1-2 % with 10 fb-1 16/09/08 A.-I.Etienvre-FAPPS 2008

Conclusion Tevatron and LHC are complementary Mass ≈ 1 % <1% @2fb-1 LHC: goals for 10fb-1 Mass ≈ 1 % <1% Cross section 10% <5% Top properties W polarisation Spin correlations Charge FCNC 40% _ -4/3 excluded 94% Limits 2% 4% -4/3 excluded Limits better x 100 Single Top Discovery @ 5? Seems difficult Precise measurement (10%) + Wt channel 16/09/08 A.-I.Etienvre-FAPPS 2008

Conclusion What could we do with the first data taken @LHC? This year: s = 10 TeV  cross section top-antitop divided by 2 Many tops should be produced And used as a tool for commissioning (JES, b-tagging) But also first cross section measurement Next year: s = 14 TeV With 1 fb-1, several measurements should be achieved Their precision relies strongly on how well we will understand our detector 16/09/08 A.-I.Etienvre-FAPPS 2008